Clinical trials to limit infarct size and to reduce mortality by decrease of oxygen demand have yielded less than satisfactory results. Recently, catheter techniques have emerged which enable improvement of oxygen supply by rapid restoration of antegrade flow in acutely occluded coronary arteries. We propose to establish a single blinded randomized trial of myocardial reperfusion in acute myocardial infarction by selective intracoronary infusion of nitroglycerin or by intracoronary infusion of streptokinase (combined with mechanical recanalization if needed). These interventions may result in: reestablishment of coronary flow; limitation of infarct size; reduction of mortality and morbidity. The primary end point will be ejection fraction on the 10th day after the intervention. It is estimated that 220 patients randomized within 3 hours after onset of infarct symptoms and 380 patients randomized after more than 3 and less than 12 hours of chest pain will be required to show significant differences between treatment groups and the control group. This will be a collaborative trial of Mount Sinai Medical Center with Mount Sinai Hospital, Elmhurst Hospital, Bronx VA Medical Center, and New York University, Bellevue Hospital. Patient acquisition will be completed within 3 years. Clinical follow-up will be extended for 2 years. Thus, the trial will be completed within 5 years after its beginning.